Protractor



C. B. GALVIN PRoTRAcToR Aug. 2, 1927.

Filed 00t- 24, 1923 'Md 737e', ArronNErS Patented Aug. 2, 1927.

UNITED STATES CHARLES B. GALVIN, OF NEWA YORK, N. Y. Y

raornacron. y

Application led October 24; 1923. Serial No.' 670,601.

This invention relates to a new and improved protractor, and has for an object the provision of a protractor whereby improved utility and accuracy for coordinating, plotting and measuring angles may be achieved.

Another object concerns the provision of means whereby by reason of the application of well known geometrical laws 'the scale of graduations on a protractor is doubled so that the readings onthe scale arev thereby caused to be much more accurate.

A further object concerns the provision of two slides on the protractor which can rela tively be adjusted and manipulated to perform various other useful functions.

The invention is illustrated in the drawings, of whichi Figure 1 is a plan view of the protractor;

Fig. 2 is a section taken on thek line 2-#2 of Fig. 1; and

Fig. 3 is a section taken on the line l3--3 of Fig. 1. n

The form of the invention shown in the drawings isa preferred form, although it is understood that modifications in the construction and arrangement of the parts and in the character of they materials used may be adopted without departing from the spirit of the invention as set forth in the appended claims. i Y

The basic characteristics of this instrument depend upon the application of two geometrical laws, the first of which is that any angle inscribed in a circle is equal to half the angle subtendedat the Center; the other law is that any angle inscribed in a semicircle is a right angle.L

The preferred form of my invention as shown in the drawings comprises a ring 1 of any suitable material provided with gradvuations 2 along its outer periphery. This ring is provided with a crossbar 3 the edge 4 of which is in line with the diameter of` the ring, and is provided witha center' line 5 intersecting the edge 4 at the 'center of the circle of graduations.- T-he ring` at one side is provided with a diametrical line 6 along which a vplotting aperture 7 v`is disposed. This aperture is provided to permit a marker point to be insert-ed therein to mark on materials beneath the protractor.

The ring` is provided with an outwardlyv extending annular flange 8 which, as shown in Fig. 2, is slightly tapered.v The ring is also provided with an outwardly extending arm 9which extends outwardly from-the ring on the sid-el opposite thaton which the u aperture 7 is disposed.- This kvarm on its outer edge is provided with aplate 9a having an aperture in which a set screw 9b' is disposed to permit the plate tobe yclamped in 'any desired position on the arm 9.` @This plate is provided with an aperture 10 ir-epresenting the position of a point a definiteV ldistance from the center 5. On this plate are two other index pointsy 11 vand 12 disposed at definite distances from the center e. The plate 9a is adjustable to aline the index points 10, 11 and 12 with the diameter of the circle represented by the edge 4 of the crossbar 3. ff

The protractor is provided with a pair ofvarms 13 and 13EL extendingfoutwardly from the ring in radial directions therefrom.

lThe arm 13 on its inner' end is provided with plates 14 and 15 lying on opposite' sides of the flange v8 and adjustably engageablel therewith by means of a screw 10 sothat the flange can be gripped bythesefplates to .holdthe arm 13 on the flange in itsl rotative movement around the centerr 5. The

arm is provided `with a straight edge 13J in v line with the radius of the circle of which the center is represented by the' numeral 5.

.On'the outer end of the arm there is fastened a platey 17 adjustable by reason of the slot and set screw 18 ina manner similar totheadjustment of the plate l9a on the arm 9. Onthis plate are disposed indicating points 21 and 22as well as an aperture 19 having an apertured plate. 20 therein,r the aperture in the plate 20 representing a point a distance from the center 5 equaltothe distance of the point 10 therefrom. @The index point 21 is equidistantfromthe center 5 Withthe index point 11, and the index point 22 is equidistant with the index point L; 12 from the center 5.' The-'rotatable arm 13 is associated in its operation with a pair of plates 24 and 25 which are disposed on opposite sides of the flange 8 adjacent the arm 13 and are held together on said fiange bythe clamping screw 26. VTheupper plate 24 of the pair of plates is provided with-an apertured stud 27 through which'ashaft 29 passes. The other end ofthis shaft is engageable with astud 28 on, the plate 14.-.

A thumbpiece 3() formed on vthe end of the shaft 29 permits it to be rotated. i This shaft is threaded into the stud 27,v and a springy 31 embraces Vthe shaft 29 between the studs 27 and 28. Byv rotating'the shaft 29after "angles can be read by considering either "other hand, the apertures 21,11 `and! 21n the outside index points 12 having clamped the plates 241 and 25 firmly in a fixed position on the fiange 8, the posi? of course, understood that the arm 13 is provided with a Vernier scale 202, so that after the plates 24 and 25 have been clamped to the flange 8 the manipulation of the shaft 29 will permit the Vernier to be properly set and read in theusual manner.

v It will be observed that the arm 13L is of a construction identical with that of arm 13, t-he parts of this construction being numbered with the same numerals as correspondin@ parts on the l arm `13 with the sutiX all after them. The operation and manipuf lation of this arm is identical with the operation and manipulation of thearm 13.

Y It will be observed that the scales on the ring 1 extend-from `a Zero point adjacent the aperture 7 in either direction around the ring and that each half of the ring is divided into 900. `By reason of the fact that each arm rotates'around the center 5, we will assume that the arm' 13, for instance, is positioned opposite the nume al 30 on the upper scale. In accordance with the fact that the numeral `30 is laid off to represent an angle of 30o, kthisjangle is formed between lines drawn, for instance, from the aperture 2O to the `aperture 10 and then"drawnfrom the aperture 1() to the aperture 7. This angle is 30", whereas theanglejdrawn between the aperture 2O and the center 5 and the aperture 7 is actually 600, in otherwords, twice the previously mentioned angle. I-Iowever,

by beingableto divide up the scale from zeroto the 30"` niark into thirty spaces 1nstead of sixty, I am ableto set-the slide of the rotatable arms with much greater accuracy. 1-

u It is -to be understooth of course, that the the apertures 20, 10 and 7 or by considering the apertures 20, 10 and 201. 'Whereas,` on the can be considered `as` those apertures through which lines are tobe drawn to lay olf the angle. It may, further, be desirable to use and 222L together vwiththe aperture 7 i Therefore, the reading of either one of the `Verniers is the measuring of the angle formed by lines drawn from one of the index pointson said Vernier apparatus to the corresponding index` pointon the arm `9 and "thence tothe aperture 7, which angle `is the angle inscribed inthe `semicircle and is half the 4angle subtended at thecenter of the circle by the same are. By reason of this application of the geometrical laws above mentioned, a geometrical magnification is oly tained in-layingolf the anglel by reason. .of

the fact thatthe diameter of the circle instead the radius is availablefor base. lurtherniore, an increased degree of refinement in the reading or setting of the Ver# nier/is obtained, because of the fact that the intercepted angle is measured by twice the jsubtended arc.

It is, of course, understood that by setting one of the verniers at Zero a triangle formed between an index point on this Vernici' `and corresponding index points on the other ver,- nier and the arm 9 will alwaysbe a right angle triangle because this triangle islinscribed in a semicircle of which the diameter 1 t-he protractor between two index points is the dia-meter of the circle. y

This device is, furthermore, useful for dropping perpendiculars, because while one vernici' may be set atzero, the other forms a right angle. The movable one may, therew fore be moved'toany convenient position and then clamped.

It will, therefore, be" observed that I have provided a simple and elicient device for the .1 u purpose of readily plotting angles-and directions. The scales used are sorelated to well knowny geometrical vlaws that the accu racy of the readings is increased twofold. The relation between the movable verniers and the diametrical base lineof the protractor is such that by settingthenr as above designated a right angle can be forme'dina variety of convenient places by. the-move ment of one of the verniers while the otherf isset. i

Itis, furthermore, to befnoted thattheflatin tude and departure of a course may bescaled directly as follows: lith the lowerverniier set on Zero and the upper Vernier-set on 'a given bearing, and with tllecrossbar set on a course, scale olf to anyconvenientscale one-half the length of the course on each ythe upper branch. The scale distance from the last-mentioned point-tto the? above-mentioned points on the diameter will then equal the latitude and departure, respectively. This is truiefor the reason that therelation of thevverniers 1, such as described,-consti 115 tutes a right angle triangle, and :the rela-A tion of the three points mentioned `constitutes a right'angle triangle` i What I claim is :d

1. A Vprotraetor which comprises a ring having a diametrical crossbar and a fixed arm extending radially'outwardat onezend of saidV crossbar, there being an index point on said arm, an arm mounted on said `iing to rotate about the center thereof and yhaving an index point thereon at the same distance e from the center of said ringas the previous ly mentioned index point. i u 2. A protractor Whichl comprises ia ring,

a diametrical cross bar securedto the ring,

v wr

a fixed arm extending radially outward from one end of said crossbar, there being an index point on said arm, a pair of arms mounted on said ring to rotate about the center thereof and adapted to rotate in opposite directions from the opposite end of said dameter7 each of said arms having an index point thereon at a distance from the center of said ring equal to the distance fromV the center of the rst-mentioned index point on the fixed arm. y

3. A protractor which comprises a ring provided With a plurality of graduations thereon, the values of said graduations being given in terms of half the angles subtended at the center, a diametrical crossbar secured to the ring, a `fixed arm extending radially outward from one end of said crossbar, a pair of arms mounted on said ring to rotate about the center thereof, there being a plurality of index points on each of said arms, each index point being at a distance from the center of said ring equal to a respective n index point on the other arm.

4:. A protractor comprising a-ring having scale graduations extending in opposite directions from the zero point, a diametrical crossbar secured to the ring,v said point l0- cated at one end of said crossbar, a fixed arm extending radially outward from the ring at the opposite end of said diameter, an arm mounted on said ring to rotate about the center thereof, there being index points on both of said arms at equal distances from the center of said ring, the graduations on said ring having values which are givenin termsof hallc the angle Asubtended at the center. Y

CHARLES B. GALVIN.- 

